310 ACUTE GENERAL INFECTIOUS DISEASES 



ings, which later become emphysematous and occur in the 

 region of a wound infected with the specific anaerobic 

 Bacillus oedematis maligni. 



Occurrence. — The disease is widely distributed. It affects 

 mostly horses, following accidental or surgical wounds. In 

 cattle it occurs from obstetrical operations, and in sheep may 

 result from cuts received during shearing. In the United 

 States it is one of the commonest wound-infection diseases 

 extant. 



Etiology. — ^The Bacillus oedematis maligni, which is found in 

 both the rod and spore stages in soil, manure (droppings), 

 dust, decomposing vegetable matter and polluted water. 



Natural Infection. — ^Horses and sheep seem most susceptible 

 to the infection, while cattle and swine offer more resistance. 

 The infection is always through a wound (surgical or acci- 

 dental) in the skin or mucous membrane. In practice malig- 

 nant edema most frequently follows surgical operations (poll 

 evil, castration, phlebotomy), the use of the unsterilized 

 hypodermic syringe, rough obstetrical manipulations, skin 

 cuts from careless shearing of sheep, etc. It may also follow 

 accidental wounds due to wood splinters, nails, or other 

 penetrating objects which carry the infection. Feeding and 

 inhalation experiments with the bacilli and spores of malig- 

 nant edema gave negative results. The intact skin and 

 mucous membrane are not infectable. Infection through a 

 necrotic area (ulcer) is probable. Normally granulating 

 wounds are, however, very resistant to infection. Inocula- 

 tions with pure cultures are not successful unless phagocytosis 

 is overcome by mechanical (sand particles) or chemical 

 agencies (lactic acid) or the toxins of other bacteria which 

 may be present (staphylococci) . 



Symptoms. — In the neighborhood of the infected wound a 

 rather diffuse, edematous swelling appears. The swelling is 

 at first painful, firm, and hot, but later becomes softer, less 

 painful, and on palpation crepitates. It spreads rapidly and 

 in a few hoiu-s can involve the whole body and head. In a 

 horse so afflicted the patient assumes the appearance of a 

 hippopotamus. With the advance of the external swelling 

 dyspnea develops with foamy nasal discharge (lung edema), 



Digitized by Microsoft® 



